Carnival Mask Sign on Bone Scan of Craniofacial Metastasis of Neuroblastoma

A craniofacial mass may cause the first clinical symptoms of malignancy. In addition, involvement of the craniofacial area may be associated with a poor prognosis or central nervous system (CNS) complications.[12] Although magnetic resonance imaging (MRI) is recommended in such cases, bone scintigraphy should also be performed since it can evaluate the bone lesions in the entire body in a single scan, in addition to detecting the lesions involving the bone cortex.

Bone scintigraphy should be performed in particular in patients with underlying hematologic malignancy or bone marrow involvement from various diseases, such as Langerhans cell histiocytosis (LCH) or neuroblastoma. In pediatric patients, neuroblastoma, LCH, and acute lymphoblastic leukemia (ALL) are the most common diseases initially manifesting with bone lesions, and bone scintigraphy is a useful modality to evaluate them. In addition, the treatment methods and prognosis are quite different between these diseases; therefore, differentiating them is important.

We describe the scintigraphy findings of the craniofacial bones in three patients, with neuroblastoma, ALL, and LCH. Case 1 was a 1-year-old girl with neuroblastoma. She presented orbital swelling, particularly on the right side. Diffusion-weighted imaging (DWI) MRI showed several hyperintensities in the cranial bones. Bone scintigraphy demonstrated high uptake especially in the periorbital craniofacial bones, compared to occipital or parietal bones. Therefore, the scintigraphic findings resembled a carnival mask [Figure 1a–c]. Ultrasonography revealed a left adrenal mass, and a surgical biopsy was performed. Based on bone scintigraphy, neuroblastoma involving the bone cortex was diagnosed.

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Figure 1 Case 1: 1-year-old girl with neuroblastoma. (a) Bone scintigraphy showing stronger tracer uptake in the periorbital craniofacial bones (arrowheads) than in other cranial bones, such as occipital or parietal bones (arrows), resulting in a carnival mask appearance. (b) DWI MRI showing several hyperintensities in the craniofacial bones (arrows). (c) Carnival mask sign. DWI: Diffusion-weighted, MRI: magnetic resonance imaging

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Case 2 was a 2-year-old boy with LCH, presenting a mass in the cranial bones. DWI-MRI showed some hyperintensities in the cranial bones. Bone scintigraphy demonstrated high uptake and lucent areas in the periorbital craniofacial bones [Figure 2a–c]. A surgical biopsy was performed on the bone lesions, and LCH was diagnosed. This patient exhibited CNS complications, including neurodegenerative syndrome and diabetes insipidus.

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Figure 2 Case 2: 2-year-old boy with LCH. (a) Bone scintigraphy showing high (arrowheads) or low (arrows) uptake in the craniofacial bones. Diffuse high uptake in the craniofacial bones is not particularly evident in the areas surrounding the orbits. (b) DWI-MRI shows minor hyperintensities in the craniofacial bones (arrows). (c) The overall appearance is not of a carnival mask. LCH: Langerhans cell histiocytosis, DWI: Diffusion-weighted, MRI: magnetic resonance imaging

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Case 3 was a 4-year-old boy with ALL, presenting with a fever of unknown origin and back pain. Bone scintigraphy showed diffuse high uptake in the cranial bones, and DWI-MRI showed minor hyperintensities at the same level [Figure 3a–c]. A bone marrow biopsy was performed, and ALL was diagnosed.

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Figure 3 Case 3: 4-year-old boy with ALL. (a) Bone scintigraphy showing similar moderate uptake in the periorbital craniofacial bones (arrowheads) and other cranial bones (arrows). (b) DWI-MRI showing minor hyperintensities in the craniofacial bones (arrows). (c) Not a carnival mask resemblance. ALL: Acute lymphoblastic leukemia, DWI: Diffusion-weighted, MRI: magnetic resonance imaging

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In the bone scintigraphy of neuroblastoma with craniofacial bone metastases, strong tracer uptake was evident, resembling a carnival mask [Figure 1a and c]. In contrast, in the two cases with LCH and ALL involving the craniofacial bones, the tracer uptake was lower than in neuroblastoma and with different distributions [Figures 2a and 3a]. Pediatric patients with neuroblastoma involving the craniofacial bones usually have a primary lesion elsewhere, such as in the retroperitoneal area.[1] These metastases may be locally aggressive, destroying the bones.[1] Neuroblastoma initially presents as a bone marrow lesion, and progressively increases in size, affecting the bone structure; bone scintigraphy shows it as strong tracer uptake. Bone metastases of neuroblastoma usually occur in the periorbital craniofacial bones, which show stronger uptake than other cranial bones.

LCH is associated with varying degrees of disease activity, and its bone imaging findings differ based on its activity.[3] LCH involving the craniofacial bones usually causes osteolytic changes, without bone repairing. Therefore, these lesions present low uptake in bone scintigraphy, showing as “cold spots.”[3] In addition, bone repairing may be detected at the boundaries of these cold spots, showing as high-uptake rims surrounding the osteolytic area.[3] Therefore, LCH scintigraphy of the craniofacial bones does not resemble a carnival mask [Figure 2a and c].

The bone changes in leukemia reportedly include a leukemic line and bone absorption at the metaphysis, sclerotic bony changes, or periosteal reaction. However, these changes represent the degree of bone metabolism; infiltration of bone marrow by leukemic cells usually shows as diffuse bone marrow. Therefore, in bone scintigraphy of leukemia, the tracer uptake in the periorbital craniofacial bones is similar to other cranial bones,[45] not presenting as a carnival mask [Figure 3a and c].

In conclusion, bone scintigraphy to evaluate malignant craniofacial lesions could provide useful differential diagnostic information.